Purification and characterization of insulin-like growth factor II (IGF II) and an IGF II variant from human placenta.

In order to purify variant IGF II peptides from human placenta, we have developed a purification procedure combining heparin affinity chromatography and cation-exchange, reversed-phase and size-exclusion HPLC. Two peptides were purified, both having apparent M(r) values of ca. 7300 Da as evaluated by SDS-PAGE. N-Terminal sequencing revealed IGF II and an IGF II variant in which Ser29 was replaced by the tetrapeptide Arg-Leu-Pro-Gly. The final yield of variant IGF II was about eight-fold lower than that of IGF II. Both pure peptides were functionally active as they bound to type I and type II IGF receptors from ovine and human placental membranes, as determined by crosslinking experiments and displacement curve studies.